Wood shake shingles, although popular in many parts of the United States, have been prohibited in some areas because of their vulnerability to a rapid spread of fire when sparks from a burning building are blown onto the roofs of neighboring buildings. Various solutions to the problem have been proposed. In U.S. Pat. No. 4,012,558, Wurman teaches a flame resistant board of bonded wood particles wherein a mixture of ammonium bromide, urea phosphate, and hexamethylene-tetramine is incorporated in the bonding agent. Urea-formaldehyde resins are preferred over the phenol-and-melamine-formaldehyde resins as the bonding agent. The swelling of the wood in water and the reduction of its bending strength, which Wurman identifies as problems associated with the use of ammonium bromide and other inorganic salts, are not fully overcome by the boards exemplifying Wurman's invention.
Libit, in U.S. Pat. No. 4,459,339, teaches the impregnation of wood shake shingles with a mixture of an acrylic monomer and a flame retardant phosphate such as bis-(2,3-dibromopropyl)phosphate. Polymerization of the monomer forms a resinous binder in which the phosphate is physically bound.
The incorporation of organophosphorous compounds in urea-formaldehyde resins, epoxy resins, acrylics, polyesters and the like is taught in U.S. Pat. Nos. 3,132,169; 3,192,242; 3,306,937; and 3,344,112 for flameproofing hardboard and other cellulosic materials.
Stauffer Chemical Company sells diethyl-N,N-bis(2-hydroxyethyl)aminomethyl phosphonate as a flame retardant agent under its Fyrol trademark. The phosphonate is designed to react as a polyol in the formation of polyurethane resins. The polyol function also takes part in the reaction when the phosphonate is introduced into the reaction mixture of melamine and formaldehyde so that the condensation product contains chemically bound phosphorus. Stauffer teaches in its product literature, however, that this phosphonate decomposes upon heating, forming acids at temperatures above 125.degree. C. (257.degree. F.). It decomposes slowly under moist alkaline conditions even at ambient temperatures according to that literature.